1. Field of the Invention
The present invention relates to a radio receiver having particular, but not exclusive, application in a digital, wide area pager.
2. Description of the Related Art
In view of the relatively small size of digital pagers there has been a desire to reduce the number of batteries carried by a pager and the objective is to have single cell operation. Accordingly the circuitry used in the pager is required to operate at about 1 volt and if a higher voltage is required then a voltage multiplier is provided. A critical part of a receiver is the frequency down-conversion stage which is normally implemented as a double-balanced mixer circuit. Double-balanced mixer circuits operating on 2 cell supplies are known per se. U.S. Pat. No 5,521,545 discloses a development of a double-balanced mixer circuit which enables it to operate at a lower voltage. An examination of the circuit disclosed in U.S. Pat. No 5,521,545 has shown that over the range of frequencies, between 150 MHz and 950 MHz, which are used by paging operators, there are frequency bands when this known double-balanced mixer circuit becomes unstable and behaves as an oscillator.